Most audio loudspeakers produce sound through the physical movement, or excursion, of a cone. Excursion limiters have been used in various products, such as audio speakers, to minimize output voltage to the speaker at high output levels. The advantage of excursion limiters over other limiting methods is that they may be tuned to have virtually no effect at low or moderate listening levels, but take effect at higher listening levels. This may help to preserve spectral quality without burdening the system's performance at low levels, and may improve sound quality at higher levels by minimizing distortion and unwanted excursion-related artifacts. It also may help extend the life of the driver by minimizing excursion-related damage.
Many components of an audio reproduction chain, notably loudspeakers and multiway loudspeaker crossover networks, introduce group delay in the audio signal. Group delay generally refers to a measure of the transmit time of a signal through a device under test (DUT), versus frequency. A number of experiments have shown that excessive group delay in a signal processing block can cause unwanted audible artifacts, especially at low frequencies. These may manifest audibly as a smearing of time response, such that the fundamentals of a bass note may sound like it has been delayed from the rest of the sound of the instrument. Exactly how much group delay is tolerable seems to depend on frequency; regardless, excessive group delay should be minimized as much as possible.
Excursion limiters may be used on the low-frequency speakers, such as a woofer, as they may allow the low frequency bandwidth to be extended. With a more standard configuration, a high-order, high pass filter may be used to protect the woofer from excessive excursion below resonance. This may be critical in a tuned enclosure such as a bass reflex or waveguide enclosure because the excursion of the driver may tend to increase very rapidly below the resonance of the system. Using an excursion limiter may allow for the use of a much more gently-sloped high pass filter, because the excursion limiter may be tuned to guarantee that there will not be any damaging excursion below resonance. An excursion limiter that uses high-Q filters may have a narrow frequency range of effectiveness, but, when used with a woofer, may have excessive group delay in that frequency range, resulting in audible time-domain transient response problems.